FAA Perspectives on Historical Wake Turbulence R&D to ... · the airport environment, and with each...

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FAA Perspectives on Historical Wake Turbulence R&D to Recent Operational Implementations

James N. Hallocka

David C. Burnhamb

Frank Y. Wangc

Copyright Form C: This material is a work of the U.S. Government and is not subject to copyright protection in the United States.

9th AIAA Atmospheric and Space Environments Conference, Denver CO, June 3-9, 2017

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Affiliationsa Consultant, Retired USDOT Volpe Center, Senior Member AIAAb SCENSI, Former USDOT Volpe Center, Senior Member AIAAc USDOT Volpe Center, Member AIAA

5 June 2017 AIAA Denver CO

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Acknowledgements –FAA Leadership Team

• Jeff Tittsworth• Paul Strande• Jillian Cheng• Wayne Gallo• Edward Johnson


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Purpose

• A major intent of this presentation is to delineate why the many years of Wake Turbulence R&D are finally yielding beneficial operational implementations.

• Highlight lessons learned from past R&D.• Going forward – NextGen and Beyond


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Some Things to Keep in Mind• Useful to note that wake turbulence separation minima is

more than just the well known in-trail separation (FAA JO 7110.65W) CSPR (Closely Spaced Parallel Runways) Intersection Departures Intersecting Runways En-Route vertical separation (ICAO Doc 9574)

• Useful to recognize that in the terminal area, FAA has an unique culture of having both VFR and IFR flights Wake separation minima is enforced on approach and at threshold

crossings, under IFR Visual approaches can be used in VMC, where pilots can assume wake

avoidance responsibility Wake separation minima is enforced when operating directly behind

under VMC and IMC However, wake solutions have been addressing both IFR and VFR

operations


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Highlights of Knowledge 1970-2000 (1/3)

• Sensors were developed to measure wake vortices in the airport environment, and with each sensor technology it leads to newer sensors and increasingly relevant knowledge1,2

• A wide array of sensors were designed and tested, but eventually three main sensor types became the work-horses at various times: Anemometers (windline 3,4) Acoustic systems (pulsed -- bistatic5 and monostatic6) Lidar (CW4,7 and pulsed4,8)


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• Confirmed many fundamental theoretical frameworks such as initial circulation (weight, speed, wingspan relationship), transport9, descent, rebound and vortex tilt10

• Recognized early from field measurements that vortices can at times last longer than separation standards11; therefore, the safety of a system does not solely rely on wake lifespan

• Established early on the sensitivity to atmospheric parameters9

• Determined departure vs arrival vortex behavior are essentially the same12


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• Introduced concept of Γ[5-15] vs Γ total and a simple vortex model that later became known as the Burnham-Hallock model13

• Established rotorcraft wake characteristics – hover vs forward flight 14

• Confirmed the onset of instability and breakup exists for OGE and NGE regions15

• Determined that vortices decay from the outside in (vorticity does not diffuse from inside out / high vs low Reynolds number influence)16

• Configuration effects17

• Proposed a range of wake severity metrics18-19


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Prior to 2000 – R&D was Mostly R

• Historical Background: No Significant Operational Changes Benefitting the NAS Prior to 2000: 30+ Years of R&D with most of that being R Earlier efforts to change standards ineffectively coordinated between

researchers and users/stakeholders Separations overall got larger with increasing R&D 20

• “Add a Mile” for Small aircraft at threshold However, resulting R&D yielded a safe system (when procedures and

wake mitigation strategies were followed)


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What Changed Over Time (1/4)

• Program Redirection (Since 2000) Focused on operationally feasible solutions using well established Wake

science to date Focused R&D for each specific defined goal Used phased approach – near, mid- to far-term goals Developed airport specific solutions instead of “One Size Fits All” Had insight that wake turbulence solutions to the National Airspace

System (NAS) do not revolve solely on wakes from Heavy aircraft Resulted on a steady evolution of solutions which increased in

complexity and applicability as they were developed


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• Advancements of Sensor and Information Technologies 24 x 7 data collection Statistically large amount of data collection now routine, including

• Seasonal and diurnal effects• Aircraft ID details down to M/M/S • Detailed aircraft speed profiles 21

Ability to collect a much rawer form of the data for subsequent post-processing and reprocessing

Ability to provide data-driven safety evidence Entire flight region of interest for safety argument/consideration can be

addressed via direct measurements• Arrival: From Stabilized Approach Point to Runway Threshold• Departure: From Rotation Point to Point of Divergence


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What Changed Over Time (3/4) --Evolution of Measurement Tools

2000+


1980s and 90s1970s

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• Stakeholder and Intra-Agency and International Involvement Intra-Agency: FAA NextGen, AFS, ATO, AOV, NATCA, ALPA, etc. all

involved from the onset International: for example, international WG established the process

and method of evaluation for addressing A-388 and B-748 wake turbulence separation minima

Safety Management System (SMS) Process – provides a rational, documentable and repeatable safety assessment

Dedicated and frequent workshops for solicitation of end-user/stakeholder feedback


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Separation Standards

• When the first wake turbulence separation standards were promulgated in 1970, the maximum certificated takeoff weight (MTOW) was used to form weight categories. Wingspan was acknowledged to be a better criterion, but its use was considered to be more complicated and MTOW was already in use by ATC.

• MTOW has served as a surrogate metric for both the wake turbulence severity generated by the lead aircraft as well as the wake encounter vulnerability of the trailing aircraft.


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MTOW vs Wingspan


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Recent Operational Implementations by the FAA

There are a number of recent operational implementations addressing the efficiency/capacity aspect of wake turbulence without compromising safety:22

Dependent Staggered Approaches to Closely Spaced Parallel Runways with 1.5 NM Diagonal Minima

FAA Order JO 7110.308 Ch3 (later consolidated with WTMA-P and re-designated as JO 7110.308A)

RECAT (Recategorization)FAA Order JO 7110.659C (for RECAT I)FAA Order JO 7110.123 (for RECAT II)

WTMA-P (Wake Turbulence Mitigation for Arrivals)FAA Order JO 7110.308A

WTMD (Wake Turbulence Mitigation for Departures)FAA Order JO 7110.316


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Design/Analysis

• RECAT – the design/analysis uses more than landing weight. In design, the lead aircraft is characterized by landing weight, wingspan and TAS at threshold and the following aircraft consideration included speed profile on approach, wake strength exposure and roll moment coefficient. 23

• WTMA-P and WTMD – the designs/analyses use local wind and in WTMD, forecast wind.


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Lessons Learned from R&D – VAS (1/2)

• The Vortex Advisory System (VAS) 24 was developed in the mid-1970s. It was a single-runway system that indicated when it was safe to reduce all wake separations for arrivals to 3 nm at the runway threshold. The algorithm was an ellipse with the semi-major axis of 12.5 knots in the headwind or runway orientation and a semi-minor axis of 5.5 knots in the crosswind orientation.


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Vortex Advisory System Ellipse


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Lessons Learned from R&D – VAS (2/2)

• A 2-knot guard band is employed to preclude rapid change of state.

• The VAS was rejected because of: All stakeholders were not fully engaged from the start Short duration of reduced separations (no forecast for availability and

persistency) Use in VMC would reduce capacity Misinterpretation of events

• The SMS process could likely have resolved these issues.

• Wake systems developed recently and under development by the FAA include forecast as well as an extensive human factors element.


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Lessons Learned from R&D – B-757 (1/3)

• Flight tests in Idaho Falls (1990) of aircraft flying past an instrumented tower 25 led to incorrect operationally relevant results.

• The B-757 was in landing configuration but flew past the tower at constant altitude. The data yielded vortices with very high core-edge tangential velocities. In addition, the attendant weather conditions were not representative of an airport operational environment.

• Regardless, the high tangential velocity results were publicized more so than the circulation, even though circulation behavior was consistent with the B-757 weight and wingspan.


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Lessons Learned from R&D – B-757 (2/3)• However, B-757’s measured tangential velocities as well

as circulation history when on a 3-degree glideslope yielded different results – the B-757 behaved similar to other Large aircraft at the time (i.e., B-727 and the lighter variant of the DC-8).

• Regardless, the B-757 was labeled a special aircraft needing special treatment.

• The accidents that occurred behind the B-757 were in VFR and the B-757 was flying higher than a normal 3-degree approach and the trailing aircraft were inside of 2.5 nm in trail and below the glide path of the B-757.

• After many years (proper analysis of airport measurements from 1999 to 2015), the additional separation behind the B-757 has been slowly reduced toward that used today behind other Large aircraft.


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Lessons Learned from R&D – B-757 (3/3)• Two major lessons: (1) The key is to collect data in as

close to the operational configuration and conditions as possible. (2) The relevant safety metric is important.

• The NTSB recommended 26 that future turbojet*, transport category aircraft should be assessed for wake turbulence characteristics during certification. The FAA pointed out that the wake characteristics are not a certification issue but are now part of analysis prior to aircraft entry into service.

• These lessons learned were carried over to the design of recent international efforts (A-388 and B-748 flight test assessments), as well as smaller wake generators.


* In the FAA vernacular “Turbojet” essentially means gas turbine engines (which includes turbojets and turbofans)

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Going Forward (Partial Topics)

• RECAT Phase III (dynamic pairwise separations)• CSPO enabled concepts• Efforts to assess wake turbulence risk (i.e., frequency

and severity of encounters) in a more absolute framework Progress made to date is in a relative safety framework -- new

procedures and systems need to be as safe as an existing system/procedure that has extensive operational experience

• ADS-B enabled weather messages for wake turbulence (ADS-Wx), such as wind, turbulence and stratification

• En-route wake turbulence mitigation


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Closing Comments (1/2)

• Wake turbulence is a rich subject that involves multiple disciplines: fluid mechanics, meteorology, flight mechanics/applied aerodynamics, instrumentation, remote sensing, human factors, etc. However, one must keep in mind that it is fundamentally an ATC/transportation and aviation safety and capacity problem.

• Even though it is a transportation problem, it still has a technical component whose current success is partially based on the collective progress over the years of researchers such as those from the AIAA community.


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Closing Comments (2/2)

• Wake Turbulence solutions are not solely a US or EU or other regional concern, rather a Global Aviation concern

• For the Global Success / Impact• Manufacturers have a role in providing aircraft performance data• Airlines and other Operators have a role in describing the importance

of an operational change and acting as an advocate • Regulators have the role of assessing the safety of a proposed change• ANSPs have the role of implementation of the proposed change in an

acceptably safe manner• Researchers have a role in developing proposed changes that are

operationally achievable, and responsive to the technical needs of the aviation authority


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References (1/7)1 Burnham, D. C., Gorstein, M., Hallock, J. N., Kodis, R., Sullivan,

T. E.. And McWilliams, I. G., “Aircraft Wake Vortex Sensing Systems,” DOT-TSC-FAA-72-13, June 1971, US DOT Transportation Systems Center, Cambridge, MA.

2 Burnham, D. C., Mackey, S., Wang, F. and Wassaf, H., “WakeTurbulence Measurements – Practical Experience, Considerations, Contributions Made to the NAS and Science to Date,” WakeNet 3 Europe – Greenwake Dedicated Workshop on Wake Vortex and Wind Monitoring Sensors in all Weather Conditions, March 2010, Palaiseau, France.

3 Sullivan, T. E. and Burnham, D. C., “Ground Wind Vortex Sensing System Calibration Tests,” FAA-80-13, February 1980, DOT Transportation Systems Center, Cambridge, MA.


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References (2/7)4 Nguyen, D. P. C., “May 26 – June 6, 1997 Wake Vortex

Measurements at John F. Kennedy Airport for a 2.02 Micron Pulsed Coherent Lidar, a 10.6 Micron CW Lidar and a Ground Wind Vortex Sensing System,” RTI/4903-032-035, August 1998, Center for Aerospace Technology, Research Triangle Institute, Hampton, VA.

5 Burnham, D. C., Kodis, R. and Sullivan, T. E., “Observations of Acoustic Ray Deflection by Aircraft Wake Vortices,” Journal Acoustical Society, Vol. 52, No. 1, Part 2, March 1972, pp. 431-433.

6 Burnham, D. C., Sullivan, T. E. and Wilk, L. S., Measurement of Wake Vortex Strength by Means of Acoustic Back Scattering, Vol. 13, No. 11, November 1976, pp. 889-894.

7 Burnham, D. C., Hallock, J. N., McWilliams, I. G., Fantasia, J. and Winston, B., “Measurements of Aircraft Wakes at 250-Meter Altitude with a 10.6-Micron CW Laser Doppler Velocimeter,” Electro-Optics Laser 78 Conf., 1978, Boston, MA.


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References (3/7)8 Hannon, S. M. and Thomson, J. A., Aircraft Wake Vortex Detection

and Measurement with Pulsed Solid-State Coherent Laser Radar,” J. Modern Optics, Vol. 41, No. 11, November 1994, pp. 2175-2196.

9 Hallock, J. N., Wood, W. D. and Spitzer, E. A., “The Motion of Wake Vortices in the Terminal Environment” AIAA/AMS Sixth Conf. on Aeronautical Meteorology, November 1974, El Paso, TX, pp. 393-398.

10 Burnham, D. C., “Effect of Ground Wind Shear on Aircraft Trailing Vortices,” AIAA Journal, Vol. 10, No. 8, August 1972, pp. 1114-1115.

11 Hallock, J. N., Winston, B. P., Burnham, D. C., Sullivan, T. E. and McWilliams, I. G., “Joint US/UK Vortex Tracking Program at London Heathrow International Airport, Vol. II: Data Analysis,” FAA-RD-&^-58.II, Nov. 1977, DOT Transportation Systems Center, Cambridge, MA.


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References (4/7)12 Hallock, J. N., "Differences Between Landing and Takeoff Wake

Vortices," Proceedings of the International Wake Vortex Meeting, TP 13166, edited by H. Posluns, Transport Canada, Montreal, Ottawa, Canada, Dec. 1997, pp. 81-82.

13 Burnham, D. C. and Hallock, J. N., “Chicago Monostatic Acoustic Vortex Sensing System: Vol. IV: Wake Vortex Decay,” FAA-RD-79-103.IV, July 1982, DOT Transportation Systems Center, Cambridge, MA.

14 Teager, S. A., Biehl, K. J., Garodz, L. J., Tymczyszym, J. J. and Burnham , D. C., “Flight Test Investigation of Rotorcraft Wake Vortices in Forward Flight,” DOT/FAA/CT-94-117, Feb. 1996, FAA Technical Center, Atlantic City, NJ.

15 Hallock, J. N. and Eberle, W. R., editors, “Aircraft Wake Vortices: a State-of-the-Art Review of the United States R&D Program,” FAA-RD-77-23, February 1977, DOT Transportation Systems Center, Cambridge, MA.


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References (5/7)16 Hallock, J. N. and Burnham, D. C., “Decay Characteristics of Wake

Vortices from Jet Transport Aircraft,” AIAA Paper 97-0060, Jan. 1997, Reno, NV.

17 Burnham, D. C. and Sullivan, T. E., “Influence of Flaps and Engines on Aircraft Wake Vortices,” Journal of Aircraft, Vol. 11, No. 9, September 1974, pp. 591-592.

18 Burnham, D. C. and Hallock, J. N., “Wake Vortex Separation Standards: Analysis Methods,” DOT/FAA/ND-97-4, May 1997, DOT Volpe National Transportation Systems Center, Cambridge, MA.

19 Anon., “Vortex Wake Turbulence, Flight Tests Conducted During 1970,” FAA-FS-71-1, February 1971, FAA Flight Standards Service, Washington, DC.

20 Hallock, J. N., “How the Present Separation Standards were Created,” 3rd Annual WakeNet2-Europe Workshop, EuroControl Experimental Centre, Britiony, France, Nov. 2005.


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References (6/7)21 Wynnyk, L., Lunsford, C. R., Tittsworth, J. A. and Pressley, S.,

“Development of Approach and Departure Aircraft Speed Profiles,” Journal of Aircraft, Vol. 54, No. 1, Jan.-Feb. 2017, pp. 94-103.

22 Tittsworth, J. A., Lang, S. R., Johnson, E. J. and Barnes, S. “Federal Aviation Administration Wake Turbulence Program – Recent Highlights,” 57th Air Traffic Control Association Annual Conference & Exposition, October 2012, Gaylord National Resort and Convention Center, Maryland.

23 Cheng, J., Tittsworth, J. A., Gallo, W. and Awwad, A., The Development of Wake Turbulence Recategorization in the United States,” AIAA Paper 2016-3434, June 2016, Washington, DC.

24 Wood, W. and Hallock, J. N., “Status of the Wake Vortex Avoidance System,”, EASCON-74 Conf., Oct. 1974, Washington, DC.


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References (7/7)25 Garodz, L. J. and Clawson, K. L., “Vortex Wake Characteristics of

B757-200 and B767-200 Aircraft Using the Tower Flyby Technique,” ERL-ARL-199, Vol. 1 and 2, Jan. 1993, NOAA Air Resources Lab, Idaho Falls, ID.

26 https://www.ntsb.gov/safety/safety-recs/recletters/A94_42_60.pdf


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Common Error: FAA test – Not NASA


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